A diffuser of that type is already known for feeding a double-headed combustion chamber, i.e. a combustion chamber having two concentric annular sets of fuel injectors. The separator comprises two circularly symmetrical surfaces of revolution that diverge downstream away from the inlet to the diffuser. That structure has a very open configuration and is for engines of large size. It is not suitable for feeding a single-head combustion chamber, in particular for an engine of relatively small size.
A diffuser is also known comprising two coaxial separators arranged one around the other to split the flow of air leaving the compressor into three coaxial annular streams, with the middle stream feeding the combustion chamber while the streams situated radially inside and radially outside the middle stream feed circuits for bypassing the combustion chamber, for cooling the walls thereof, and the walls of a turbine arranged at the outlet from the combustion chamber. That known diffuser is designed for an engine of large size and is not suitable for use in an engine of relatively small size.